The U.S. National Security Agency (NSA)’s data collection program has been an effective tool to enhance the country’s security but some elements of the cyber-spying raises privacy concerns, a U.S. federal privacy watchdog said in a report.

Privacy issues have become a hot topic since former NSA contractor Edward Snowden exposed the spy agency’s phone and Internet spying programs.

But the program has allowed the government to collect a greater range of foreign intelligence “quickly and effectively,” the Privacy and Civil Liberties Oversight Board said in a report released on Wednesday.

It added, however, that certain aspects of the program raise questions about whether its impact on U.S. persons pushes it over the edge into “constitutional unreasonableness”.

The watchdog said it was concerned about the incidental collection of U.S. persons’ communications and the use of queries to search the information collected under the program for the communications of specific U.S. persons.

The program, part of the United States’ Foreign Intelligence Surveillance Act (FISA), collects electronic communications, including telephone calls and emails, where the target is a non-U.S. citizen located outside the United States.

The board, set up in 2004, is an independent government agency within the executive branch that advises the U.S. president and Congress on how to ensure that counter-terrorism operations also protect Americans’ privacy.

The report was the oversight board’s second involving NSA programs. In January the watchdog said that NSA’s bulk collection of phone records provides only minimal benefits to countering terrorism, is illegal and should end.

The five-member board also offered several recommendations so that the program could strike a better balance between privacy, civil rights, and national security.